NCERT Solutions Class 10 Science How do Organisms Reproduce class 8

NCERT Solutions Class 10 Science How do Organisms Reproduce class 8 

In text questions

Page no. 128

1. What is the important of DNA copying in reproducation?

Ans: DNA copying is very important to produce organisms which are similar to their parents.

In the process of reproduction, there must be a transfer of the blueprint of the body design from parent to their off springs.
 2. Why is variation beneficial to the species but not necessarity for the individual?
Ans: Variations are beneficial to the species than individual because sometimes for a species, the enviromental conditions change so drastically that their survival bacomes difficult. For example, if the temperature of water increases suddenly, then most of the bacteria living in that are resistant to heat would be able to survive. However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus these variants help in the survival of the species. However, all variations are not necessarily beneficial for the individual organisms.
Page no. 133
1. How does binary fission differ from multiple fission?
Ans:In binary fission a single cell divides into two equal halves. Amoeba and bacteria divide by binary fission.
In multiple fission, a single cell divides into many daughter cells simultaneously. Plasmodium divide by multiple fission.
2. How will an organism be benefited if it reproduce through spores?
Ans: Advantages of spore formation:-

• Large numbers of spores are produced in one sporangium.
• Spores are distributed easily by air to far-off places to avoid competition at one place.
• Spores are covered by thick walls to prevent dehydration under unfavourable condition

3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration? 

Ans: Higher complex organisms cannot give rise to new individuals through regeneration because complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerated their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.
4. Why is vegetative propagation practised for growing some types of plants?
Ans: Vegetative propagation is practiced for growing some types of plants because of following advantages:

• It is used to grow a plant in which viable seeds are not formed or very few seeds are produced such as Orange, Banana, Pineapple.
• It helps to introduced  plants in new areas where the seed germination fails to produce plants due to change in environmental factors and the soil.
• It is more rapid, easier and cheaper method.
• By this method a good quality of a race or variety can be preserved.

5. Why is DNA copying an essential part of the process of reproduction?

Ans:  For an organism to produce its own kind, it becomes necessary that the offspring get similar DNA as in parents. DNA replication is the way through which a cell makes additional copies of DNA so that they can be transferred to the offspring.

Page no. 140

1. How is the process of pollination different from fertilization?

Ans:

Pollination is the process of transfer of pollens from anther to stigma. It occurs with the

help of certain pollinators such as air, water, birds, or some insects.

Fertilization, on the other hand, is the fusion of the male and female gametes. It occurs

inside the ovule and leads to the formation of zygote.

Question 2:

What is the role of the seminal vesicles and the prostate gland?

Answer 2:

The secretions from seminal vesicles and prostate glands lubricate the sperms and provide

a fluid medium for easy transport of sperms. Their secretion also provides nutrient in the

form of fructose, calcium, and some enzymes.

Question 3:

What are the changes seen in girls at the time of puberty?

Answer 3:

Secondary sexual characteristics in girls:

• Increase in breast size and darkening of skin of the nipples present at the tips of

the breasts.

• Appearance of hair in the genital area.

• Appearance of hair in other areas of skin like underarms, face, hands, and legs.

• Increase in the size of uterus and ovary.

• Beginning of menstrual cycle.

• More secretion of oil from the skin, which results in the appearance of pimples.

Question 4:

How does the embryo get nourishment inside the mother’s body?

Answer 4:

The embryo develops inside the mother’s body for about nine months. Inside the uterus,

the outer tissue surrounding the embryo develops finger-like projections called villi. These

villi are surrounded by uterine tissue and maternal blood. They provide a large surface

area for exchange of oxygen and nutrients. Also, there is a special tissue called placenta,

which is embedded in the uterine wall. The embryo receives the oxygen and nutrients

from the mother’s blood via the placenta. The waste materials produced by the embryo

are also removed through the placenta.

Question 5:

If a woman is using a copper−T, will it help in protecting her from sexually transmitted

diseases?

Answer 5:

No. Using a copper-T will not provide a protection from sexually transmitted diseases, as

it does not prevent the entry of semen. It only prevents the implantation of the embryo

in the uterus.

Excercise

Question 1:

Asexual reproduction takes place through budding in

(a) amoeba.

(b) yeast.

(c) plasmodium.

(d) leishmania.

Answer 1:

(b) Asexual reproduction takes place through budding in yeast.

Question 2:

Which of the following is not a part of the female reproductive system in human beings?

(a) Ovary

(b) Uterus

(c) Vas deferens

(d) Fallopian tube

Answer 2:

(c) Vas deferens is not a part of the female reproductive system in human beings.

Question 3:

The anther contains

(a) sepals.

(b) ovules.

(c) carpel.

(d) pollen grains.

Answer 3:

(d) The anther contains pollen grains.

Question 4:

What are the advantages of sexual reproduction over asexual reproduction?

Answer 4:

Advantages of sexual reproduction:

 In sexual reproduction, more variations are produced. Thus, it ensures survival of

species in a population.

 The new formed individual has characteristics of both the parents.

Variations are more viable in sexual mode than in asexual one. This is because in

asexual reproduction, DNA has to function inside the inherited cellular apparatus.

Question 5:

What are the functions performed by the testis in human beings?

Answer 5:

The testes are the male reproductive organs that are located outside the abdominal cavity

within a pouch called scrotum.

Functions of testes:

 Produce sperms

 Produce a hormone called testosterone, which brings about secondary sexual

characters in boys.

Question 6:

Why does menstruation occur?

Answer 6:

Menstruation is a process in which blood and mucous flows out every month through the

vagina. This process occurs every month because one egg is released from the ovary every

month and at the same time, the uterus (womb) prepares itself to receive the fertilized

egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to

nourish the embryo. If the egg does not get fertilised, then the lining of the uterus breaks

down slowly and gets released in the form of blood and mucous from the vagina.

Question 7:

Draw a labelled diagram of the longitudinal section of a flower.

Answer 7:

Question 8:

What are the different methods of contraception?

Answer 8:

The contraceptive methods can be broadly divided into the following types:

Natural method: It involves avoiding the chances of meeting of sperms and ovum.

In this method, the sexual act is avoided from day 10th to 17th of the menstrual

cycle because during this period, ovulation is expected and therefore, the chances

of fertilization are very high.

Barrier method: In this method, the fertilization of ovum and sperm is prevented

with the help of barriers. Barriers are available for both males and females.

Condoms are barriers made of thin rubber that are used to cover penis in males

and vagina in females.

Oral contraceptives: In this method, tablets or drugs are taken orally. These

contain small doses of hormones that prevent the release of eggs and thus

fertilization cannot occur.

Implants and surgical methods: Contraceptive devices such as the loop or

Copper-T are placed in uterus to prevent pregnancy. Some surgical methods can

also be used to block the gamete transfer. It includes the blocking of vas deferens

to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes

of the female can be blocked so that the egg will not reach the uterus known as

tubectomy.

Question 9:

How are the modes for reproduction different in unicellular and multicellular organisms?

Answer 9:

In unicellular organisms, reproduction occurs by the division of the entire cell. The modes

of reproduction in unicellular organisms can be fission, budding, etc. whereas in

multicellular organisms, specialised reproductive organs are present. Therefore, they can

reproduce by complex reproductive methods such as vegetative propagation, spore

formation, etc. In more complex multicellular organisms such as human beings and plants,

the mode of reproduction is sexual reproduction.

Question 10:

How does reproduction help in providing stability to populations of species?

Answer 10:

Living organisms reproduce for the continuation of a particular species. It helps in

providing stability to the population of species by producing a new individual that

resembles the parents. This is the reason why cats give birth to only cats or dogs give

birth to only dogs. Therefore, reproduction provides stability to populations of dogs or cats

or any other species.

Question 11:

What could be the reasons for adopting contraceptive methods?

Answer 11:

Contraceptive methods are mainly adopted because of the following reasons:

(i) To prevent unwanted pregnancies.

(ii) To control population rise or birth rate.

(iii) To prevent the transfer of sexually transmitted diseases.